Writing a simple MicroProfile application (2): Adding persistence

In my writing a simple MicroProfile application article, I went through the steps in creating a simple meeting coordination application. In this article I’ll take you through how to update that MicroProfile application to add persistence.

At the time this article was written the MicroProfile has not defined a persistence mechanism. This isn’t because MicroProfile doesn’t view persistence as important, but indicates the many equally valid choices that could be made for persistence in microservices. In this article, I use MongoDB but there are other equally valid options like JPA, Cloudant, Cassandra.

The sample application solves a real problem that the Liberty development team had. The globally-distributed Liberty development team has a lot of online meetings using IBM Connections Cloud Meetings. IBM Connections Cloud provides meeting rooms to individual employees, which is a problem for team meetings if the person who initially set up the meeting room can’t make it (e.g. they were called into another meeting, are on vacation, or sick). The sample application provides a single URL for a meeting, which can then be ‘started’ by one person and everyone else gets redirected.

The meeting application is available in GitHub. Each branch in the repository maps to an article. The starting point for the app for this article is branch part1. By the end of this article, your code should match the code in branch part2.

This article assumes you are using Eclipse and WebSphere Developer Tools (WDT). To install WDT, download and start Eclipse, then drag and drop
on to the toolbar to start the WDT installer.

Getting the source into Eclipse from GitHub

The files for this application are available in GitHub. To follow this article, you want to clone the repository, check out the part1 branch of the repository, and import the project into Eclipse. You can do this from the command line or directly from Eclipse.

From the command line

If you prefer to clone the Git repository from the command line:

Run the following commands:

git clone https://github.com/WASdev/sample.microprofile.meetingapp.git
cd sample.microprofile.meetingapp
git checkout part1

In Eclipse, import the project as an existing project.

From Eclipse

If you prefer to clone the Git repository from Eclipse:

In Eclipse, switch to the Git perspective.
Click Clone a Git repository from the Git Repositories view.
Enter URI https://github.com/WASdev/sample.microprofile.meetingapp.git
Click Next, then click Next again accepting the defaults.
From the Initial branch drop-down list, click part1.
Select Import all existing Eclipse projects after clone finishes, then click Finish.
Switch to the Java EE perspective.

The meetings project is automatically created in the Project Explorer view.

Installing MongoDB

Depending on what platform you are on the installation instructions may be different. For this exercise you should get the community version of MongoDB from the MongoDB download-center.

Once installed you can run the MongoDB database daemon using:

mongod -dbpath <path to database>

The database needs to be running for the application to work. If it isn’t running there will be a lot of noise in the server logs.

Updating the application to compile against the MongoDB API

To start writing code, the Maven pom.xml needs to be updated to indicate the dependency on MongoDB:

Open the pom.xml.
On the editor select the Dependencies tab.
On the dependencies tab there are two sections, one for Dependencies, and the other for Dependency Management. Just to the right of the Dependencies box there is a Add button. Click the Add button.
Enter a groupdId of org.mongodb
Enter a artifactId of mongo-java-driver
Enter a version of 2.14.3
In the scope drop-down, select provided. This will allow the application to compile, but will prevent the Maven WAR packager putting the API in the WAR file. Later the build will be configured to make it available to the server.
Click OK
Save the pom.xml.

Update MeetingsUtil to convert between MongoDB and JSON-Processing objects

When updating the application, we need to convert between the MongoDB representation of data and the JSON-Processing one. Rather than scatter this around this can be placed in the MeetingsUtil class:

Open the MeetingsUtil class from meetings > Java Resources > src/main/java > net.wasdev.samples.microProfile.meetings > MeetingsUtil.java
The first method that is needed takes a MongoDB DBObject and returns a JsonObject. At the beginning of the file, after the class definition, add the method declaration:
```
    public static JsonObject meetingAsJsonObject(DBObject obj) {
        // method body will go here
    }
```
This introduces one new class, the DBObject class is in the com.mongodb package:
```
    import com.mongodb.DBObject;
```
The first step in creating a new JsonObject is to create a JsonObjectBuilder using the JSON class. All of these are already used in the class so no new imports will be required. Add the following line to the start of the method:
```
    public static JsonObject meetingAsJsonObject(DBObject obj) {
        JsonObjectBuilder builder = Json.createObjectBuilder();
```
The JSON object for a meeting uses a field called id. MongoDB uses _id for the same function, so id in JSON will map to _id in MongoDB. To extract the id field from the DBObject and add it to the JSON, add this line to the method:
```
 
        builder.add("id", (String) obj.get("_id"));
```
The title field can be directly mapped from JSON to the MongoDB object. The title is a String but, to ensure the right add method is called, cast it to a String. Add this line:
```
         builder.add("title", (String) obj.get("title"));
```
The duration field is a Long. As before it needs to be cast to a Long to ensure the right add method is called:
```
        builder.add("duration", (Long) obj.get("duration"));
```
If a meeting is running it’ll have a meetingURL field. If it isn’t running it’ll return null. If there is no meetingURL field, we don’t want to add it to the meeting returned so we want to only add if meetingURL is non-null. Add this:
```
        String meetingURL = (String) obj.get("meetingURL");
        if (meetingURL != null)
            builder.add("meetingURL", meetingURL);
```
Finally we need to return a JsonObject. This can be obtained by calling the build method on the JsonObjectBuilder. Add this:
```
        return builder.build();
```
Next, we need a method that does the opposite, mapping from a JsonObject to a DBObject. This method serves two purposes: It creates a new DBObject and it merges a JsonObject to an existing DBObject, so that it has two parameters rather than one. After the end of the previous method add this:
```
    public static DBObject meetingAsMongo(JsonObject json, DBObject mongo) {
        // method body will go here
    }
```
The first thing to do in this new method is check if the DBObject passed in is null. If it is null, a new DBObject is created. DBObject is abstract so a BasicDBObject is what will be instantiated. At the beginning of the method add this (there will be a compile error after this but don’t worry, it’ll be fixed soon):
```
        if (mongo == null) {
            mongo = new BasicDBObject();
```
Next, the id needs to be moved from the JsonObject to the new DBObject. This should only be done when a new DBObject is created because, otherwise, a disconnect between the URL and the JsonObject could result in an id being incorrectly overwritten. Add this:
```
            mongo.put("_id", json.getString("id"));
        }
```
This introduced a new class, the BasicDBObject which is in the com.mongodb package but needs to be imported:
```
    import com.mongodb.BasicDBObject;
```
The title field is a direct mapping from the JsonObject to the DBObject but the JsonObject contains a JsonString which needs to be converted to a String. The toString method can’t be used for this because it wraps the String literal with quotes, which isn’t required here. Fortunately JsonObject provides a convenient getString method for this:
```
        mongo.put("title", json.getString("title"));
```
The duration field is also a direct mapping but it’s a JsonNumber in the JsonObject, which needs to be converted to a Long to go into the DBObject:
```
       mongo.put("duration", ((JsonNumber) json.get("duration")).longValue());
```
This introduced the JsonNumber, which needs to be imported:
```
import javax.json.JsonNumber;
    
```
We want to get the meetingURL but, since it might not be there, you can’t use the getString method because it’ll throw a NullPointerException if there is no field with that name. To get around this, use the get method, which returns a JsonString. A null check can then be performed and only if it is non-null will it be added to the JSON. The getString method must be used since toString wraps the string in quotes:
```
       JsonString jsonString = json.getJsonString("meetingURL");
        if (jsonString != null) {
            mongo.put("meetingURL", jsonString.getString());
        }
 
```
This introduced the jsonString, which needs to be imported:
```
    import javax.json.JsonString;
```
Finally return the mongo object and save the file.
```
       return mongo;
```

Updating the MeetingManager

The MeetingManager currently makes use of a ConcurrentMap to store the meetings. All the code that integrates with this needs to be updated. In this section this is done one step at a time; as a result there will be compililation errors until you get to the end:

Open the MeetingManager class from meetings > Java Resources > src/main/java > net.wasdev.samples.microProfile.meetings > MeetingManager.java.

After the class definition delete the following line from the file:

	private ConcurrentMap<String, JsonObject> meetings = new ConcurrentHashMap<>();

To interact with MongoDB, an instance of DB needs to be injected. This can be done using the @Resource annotation which can identify which resource from JNDI to inject. Add the code where the ConcurrentMap was removed (in the previous step):
```
	@Resource(name="mongo/sampledb")
	private DB meetings;
```
This pulls in two new classes. The MongoDB DB class and the Java EE @Resource annotation. These need to be imported:
```
    import javax.annotation.Resource;
    import com.mongodb.DB;
```
MongoDB stores entries in a collection in the database. The first thing to do when writing or reading is to select the collection. To simplify code later on, let’s create a convenience method to get the collection:
```
    public DBCollection getColl() {
        return meetings.getCollection("meetings");
    }
```
This introduces a new class, the DBCollection class, which is in the com.mongodb package. This needs to be imported:
```
    import com.mongodb.DBCollection;
```
Find and edit the add method:
1. Remove the method body from the add method. This will be replaced to update the database.
```
    public void add(JsonObject meeting) {
        // code will be added here
    }
```
2. First get the collection.
```
        DBCollection coll = getColl();
    
```
3. The method is given a JsonObject and we need a DBObject for mongoDB, so we need to convert. The API can take an existing entry from the database, so first lets see if we can find something from the database using the findOne method:
```
        DBObject existing = coll.findOne(meeting.getString("id"));
```
4. This introduces a new class, the DBObject class which is in the com.mongodb package. This needs to be imported:
```
    import com.mongodb.DBObject;
```
5. Next call the MeetingsUtil convenience method to convert from JsonObject to DBObject:
```
        DBObject obj = MeetingsUtil.meetingAsMongo(meeting,  existing);
```
6. Finally save the new or changed DBObject back into the database:
```
        coll.save(obj);
```
Find and update the get method:
1. Remove the method body from the get method (this will be replaced to fetch from the database):
```
    public JsonObject get(String id) {
        // code will be added here
    }
```
2. To get a single entry the collection needs to be obtained, an entry found by id, and then converted to a JsonObject using the utility method created earlier. Add the following line to the get method:
```
 
        return MeetingsUtil.meetingAsJsonObject(getColl().findOne(id));
```
Find and update the list method. The list method is slightly more complicated to update. The general structure stays the same but for loop will change. To iterate over entries in a collection a DBCursor is used and that returns a DBObject. The DBObject then needs to be converted to a JsonObject. Replace the existing loop that looks like this:
```
        for (JsonObject meeting : meetings.values()) {
            results.add(meeting);
        }
    
```
with this one
```
        for (DBObject meeting : getColl().find()) {
            results.add(MeetingsUtil.meetingAsJsonObject(meeting));
        }
```
Find and update the startMeeting method:
1. This change will radically simplify the code because there is no need to create and merge multiple JsonObjects. Instead, you can simply add the meetingURL to the existing DBObject. The id and url will still need to be fetched from the JsonObject. Remove the following lines from the startMeeting method:
```
        JsonObject existingMeeting = meetings.get(id);
        JsonObject updatedMeeting = MeetingsUtil.createJsonFrom(existingMeeting).add("meetingURL", url).build();
        meetings.replace(id, existingMeeting, updatedMeeting);
```
2. After the id and url are fetched, replace the removed code with the following four lines to get a collection, find the meeting entry, set the meetingURL, and then save it back to the database:
```
        DBCollection coll = getColl();
        DBObject obj = coll.findOne(id);
        obj.put("meetingURL", url);
        coll.save(obj);
```
Save the file.

The MeetingManager is now able to persist to a MongoDB database and back. However, the server still needs to be configured to enable it. This consists of two parts: First, server configuration and, second, getting the server runtime set up.

Updating the Server Configuration

The server configuration is part of the project so first let’s configure that:

Open the server.xml from src > main > liberty > config > server.xml.
There are several lines commented out. These need to be uncommented and then modified. The following lines should have the surrounding comment markers removed:
```
    <featureManager>
        <feature></feature>
    </featureManager>
```

Between the open and close feature tag add mongodb-2.0. It should look like this:

    <featureManager>
        <feature>mongodb-2.0</feature>
    </featureManager>

A shared library needs to be defined to be used by the application and the runtime for defining the MongoDB resources:
```
    <library id="mongodriver">
      <file name="${shared.resource.dir}/mongo-java-driver.jar"/>
    </library>
```

Next the mongo needs to be defined. This tells the server where the mongo server instance is running:

    <mongo id="mongo" libraryRef="mongodriver">
      <ports>27017</ports>
      <hostNames>localhost</hostNames>
    </mongo>

Next, define the database:

    <mongoDB databaseName="meetings" jndiName="mongo/sampledb" mongoRef="mongo"/>

Finally, configure the application so it can see the MongoDB classes:

    <webApplication location="meetings-${project.version}.war">
      <classloader commonLibraryRef="mongodriver"/>
    </webApplication>

Save the file.

The next step is to configure the Maven build to make sure all the resources end up in the right place.

Updating the Maven POM

The Maven POM needs to be updated to do a few things: It needs to copy the MongoDB Java driver into the Liberty server, define an additional bootstrap property, copy the application to a different location, and ensure that the mongodb-2.0 feature is installed:

Open the pom.xml in the root of the project.
Select the pom.xml tab in the editor.

Copy the MongoDB Java driver

Search the file for the string maven-dependency-plugin you should see this in the file:

                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-dependency-plugin</artifactId>
                <version>2.10</version>
                <executions>
                    <execution>
                        <id>copy-server-files</id>
                        <phase>package</phase>
                        <goals>
                            <goal>copy-dependencies</goal>
                        </goals>
                        <configuration>
                            <includeArtifactIds>server-snippet</includeArtifactIds>
                            <prependGroupId>true</prependGroupId>
                            <outputDirectory>${project.build.directory}/wlp/usr/servers/${wlpServerName}/configDropins/defaults</outputDirectory>
                        </configuration>
                    </execution>
                </executions>

This is copying server snippets from dependencies into the server configuration directory. We are going to add to it instructions to download the mongo-java-driver, copy it to the usr/shared/resources folder, and strip the version off the JAR file name. This last part means we don’t have to remember to update the server.xml every time the dependency version is upgraded.

To add these additional instructions, add the following lines after the </execution> closing tag:

                    <execution>
                        <id>copy-mongodb-dependency</id>
                        <phase>package</phase>
                        <goals>
                            <goal>copy-dependencies</goal>
                        </goals>
                        <configuration>
                            <includeArtifactIds>mongo-java-driver</includeArtifactIds>
                            <outputDirectory>${project.build.directory}/wlp/usr/shared/resources/</outputDirectory>
                            <stripVersion>true</stripVersion>
                        </configuration>
                    </execution>

Place `project.version` into `bootstrap.properties`

The server.xml references the WAR by artifact name and version. The version is referenced using a variable which needs to be provided to the server. This can easily be done using the bootstrap.properties:

Search the pom.xml file for the string <bootstrapProperties>. You should see this in the file:

                    <bootstrapProperties>
                        <default.http.port>${testServerHttpPort}</default.http.port>
                        <default.https.port>${testServerHttpsPort}</default.https.port>
                    </bootstrapProperties>

Before the closing </bootstrapProperties> add the following line:

                        <project.version>${project.version}</project.version>

Copy the application to the `apps` folder

The Maven POM deploys the application into the dropins folder of the Liberty server but this doesn’t allow a shared library to be used. So, instead, the application needs to be copied to the apps folder:

Search in the pom.xml for the string ‘dropins’, you should see this:

                        <goals>
                            <goal>copy-resources</goal>
                        </goals>
                        <configuration>
                          <outputDirectory>${project.build.directory}/wlp/usr/servers/${wlpServerName}/dropins</outputDirectory>

Update the word dropins to be apps. It should look like this:

                        <configuration>
                          <outputDirectory>${project.build.directory}/wlp/usr/servers/${wlpServerName}/apps</outputDirectory>

Install the `mongodb-2.0` feature from the Liberty repository

The mongodb-2.0 feature is not in the Liberty server installations that are stored in the Maven repository so it needs to be downloaded from the Liberty repository at build time:

Search the pom.xml for the string package-server, you should see this:

                    <execution>
                        <id>package-app</id>
                        <phase>package</phase>
                        <goals>
                            <goal>package-server</goal>
                        </goals>
                    </execution>
                  </executions>

Just before the </executions> tag, add the following lines to cause the mongodb-2.0 feature to be installed:

                    <execution>
                        <id>install-feature</id>
                        <phase>package</phase>
                        <goals>
                            <goal>install-feature</goal>
                        </goals>
                        <configuration>
                            <features>
                                <acceptLicense>true</acceptLicense>
                                <feature>mongodb-2.0</feature>
                            </features>
                        </configuration>
                    </execution>

Save the pom.xml.

Running the application

There are two ways to get the application running from within WDT:

The first is to use Maven to build and run the project:
1. Run the Maven install goal to build and test the project: Right-click pom.xml in the meetings project, click Run As… > Maven Build…, then in the Goals field type install and click Run. The first time you run this goal, it might take a few minutes to download the Liberty dependencies.
2. Run a Maven build for the liberty:start-server goal: Right-click pom.xml, click Run As… > Maven Build, then in the Goals field, type liberty:start-server and click Run. This starts the server in the background.
3. Open the application, which is available at http://localhost:9080/meetings/.
4. To stop the server again, run the liberty:stop-server build goal.
The second way is to right-click the meetings project and select Run As… > Run on Server but there are a few things to note if you do this. WDT doesn’t automatically add the MicroProfile features as you would expect so you need to manually add those. Also, any changes to the configuration in src/main/liberty/config won’t be picked up unless you add an include.

Find out more about MicroProfile and WebSphere Liberty.

Writing a simple MicroProfile application (4): Using WebSockets and CDI events

by Alasdair on March 29, 2017 in Coding, Java EE

Alasdair takes his simple MicroProfile application and adds WebSockets and CDI Events to notify the client about changes to the meeting. All code is in GitHub.

Continue reading Writing a simple MicroProfile application (4): Using WebSockets and CDI events

Writing a simple MicroProfile application (3): Using Java EE concurrency

by Alasdair on March 22, 2017 in Coding, Java EE

Alasdair takes his simple MicroProfile application and adds persistence using MongoDB as the persistence mechanism. All code is in GitHub.

Continue reading Writing a simple MicroProfile application (3): Using Java EE concurrency

Writing a simple MicroProfile application (1)

by Alasdair on January 11, 2017 in Coding, Java EE

Alasdair introduces MicroProfile by explaining how to write a simple application based around the mundane but real-life requirement to book meetings.

Continue reading Writing a simple MicroProfile application (1)

Writing a simple MicroProfile application (2): Adding persistence

Getting the source into Eclipse from GitHub

From the command line

From Eclipse

Installing MongoDB

Updating the application to compile against the MongoDB API

Update MeetingsUtil to convert between MongoDB and JSON-Processing objects

Updating the MeetingManager

Updating the Server Configuration

Updating the Maven POM

Copy the MongoDB Java driver

Place `project.version` into `bootstrap.properties`

Copy the application to the `apps` folder

Install the `mongodb-2.0` feature from the Liberty repository

Running the application

Related articles

Writing a simple MicroProfile application (4): Using WebSockets and CDI events

Writing a simple MicroProfile application (3): Using Java EE concurrency

Writing a simple MicroProfile application (1)

Join The Discussion Cancel reply

Getting the source into Eclipse from GitHub

From the command line

From Eclipse

Installing MongoDB

Updating the application to compile against the MongoDB API

Update MeetingsUtil to convert between MongoDB and JSON-Processing objects

Updating the MeetingManager

Updating the Server Configuration

Updating the Maven POM

Copy the MongoDB Java driver

Place project.version into bootstrap.properties

Copy the application to the apps folder

Install the mongodb-2.0 feature from the Liberty repository

Running the application

Related articles

Writing a simple MicroProfile application (4): Using WebSockets and CDI events

Writing a simple MicroProfile application (3): Using Java EE concurrency

Writing a simple MicroProfile application (1)

Join The Discussion Cancel reply

Place `project.version` into `bootstrap.properties`

Copy the application to the `apps` folder

Install the `mongodb-2.0` feature from the Liberty repository